1. Field of the Invention
This invention relates generally to continuously variable transmissions, and more particularly, to a variable V-belt type continuously variable transmission for automobiles.
2. Description of the Prior Art
In order to obtain greater fuel efficiency and to minimize the weight and cost of a conventional automatic transmission of an automobile, several attempts have been made to replace the conventional automatic transmission with a variable V-belt type continuously variable transmission (hereinafter referred to as CVT) which is lighter and less complex in structure.
However, such V-belt type CVT can obtain only 4:1 to 5:1 overall drive ratios which correspond to the belt ratios, such as, for example, the ratio of the maximum effective pitch diameter of the belt on one sheave to the minimum pitch diameter of the belt on the other sheave or vice versa.
In an automobile using the belt type CVT, however, the drive ratio should have at least a minimum ratio of 9:1 considering the fuel efficiency and engine controls. Most of the above-noted conventional CVTs have to have an auxiliary speed change gear mechanism in addition to a variable V-belt in order to obtain a wide range of drive ratios. One of the above-described attempts is shown in a DOE contract (DE-AC02-CS52749). According to this V-belt CVT, any desired range of drive ratio (up to .infin.:1) can be obtained. However, in this attempt the belt is required to have a very high durability because of the large load exerted thereon.